On motor vehicles such as automobiles, there have been employed a set of constant velocity joints for transmitting drive power from an engine through a shaft to axles. Each constant velocity joint comprises an outer member, an inner member, and a torque transmitting member disposed between the outer and inner members for transmitting torque between the outer and inner members. The constant velocity joint includes a shaft/hub unit having a tooth assembly which comprises a shaft tooth section on the shaft and a hub tooth section on a hub, the shaft tooth section and the hub tooth section being held in mesh with each other.
In recent years, there have been demands for efforts to reduce circumferential backlash of constant velocity joints which is caused by the chattering of the power transmitting system. Heretofore, attempts have been made to reduce backlash between the inner ring and the shaft with a constant velocity joint having shaft serrations tilted at a torsional angle. Depending on the direction of the torsional angle and the direction of the torque load, the mechanical strength and service life of the inner ring and the shaft are likely to vary from product to product.
In the art of gears, technical concepts for crowning tooth surfaces have been disclosed in Japanese Laid-Open Patent Publication No. 2-62461, Japanese Laid-Open Patent Publication No. 3-69844, and Japanese Laid-Open Patent Publication No. 3-32436, for example.
The applicant of the present application has proposed a spline shaft wherein the crowning top is positioned where the stress is minimized when torque is applied to a region where, the spline shaft and a constant velocity joint mesh with each other, thereby preventing the stress from concentrating on certain regions and simplifying the overall structure of the spline shaft (see Japanese Laid-Open Patent Publication No. 2001-287122).